Pitch control in pulp and papermaking



United States Patent 3,274,050 PITCH CONTROL IN PULP AND PAPEAKING Stanley J. Buckman, John D. Pera, and William P. Purcell, Memphis, Tenn, assignors to Buckman Laboratories, Inc., Memphis, Tenn., a corporation of Tennessee N0 Drawing. Filed Apr. 29, 1963, Ser. No. 276,199 12 Claims. (Cl. 162-190) The present invention relates to compositions and methods for the control of pitch problems encountered in the papermaking processes.

Most of the important woods used as the source of fibers for the manufacture of paper contain at least some natural resins composed of resin acids, fatty acids and fatty esters, and unsaponifiable materials which may present problems in the pulp and papermaking process. However, the most important problems which are frequently described as pitch troubles are encountered with the coniferous, or so-called softwoods, since these woods usually contain more resins than the hardwoods. The resins contributing to these problems are distributed throughout certain cells in the wood and are released from the cells to varying degrees by different pulping and refining processes. In general, alkaline cooking converts the resins to less troublesome compound which may be more or less completely removed by washing the pulp. In contrast, however, severe pitch problems are encountered, particularly with pulp produced by acidic processes, such as sulfite cooking, and to a lesser extent with pulp produced by mechanical methods (groundwood).

The deposits described as pitch normally are sticky, tacky aggregations of the small globules of the natural resins freed from the wood cells in the pulping processes. Other components of the paper furnish in addition to fibers, such as fillers, pigments, sizing materials, defoamers, wet strength resins, retention aids, fiber bonding agents, etc., may be entrained or otherwise become part of the socalled pitch deposits which accumulate on the surfaces of screens, chests, pipes, the wire of the paper machines on which the sheet of the paper is formed, in the wet felts, on the presses, and in the dryers and calender stacks. Aggregations of pitch and other materials in the paper furnish also may be carried along with the furnish and grow in size as they move along in the papermaking process. These, and the deposits Which accumulate throughout the paper machine systems, break loose periodically to cause spots and holes in the sheet of paper, poor formation of the sheet over areas on the paper machine wire partially plugged (blinded) by pitch and entrained materials, as well as cause breaks of the sheet so that it must be rethreaded through the dryer section before production of paper can be resumed. Pitch and entrained materials accumulating in wet felts of the paper machines also reduce the water removing ability of the felts and thereby increase the amount of water which must be removed by the many times more expensive process of evaporating water from the sheet in the dryer section of the paper machines.

.To cope with pitch problems, various measures have been employed all along the production line from wood procurement and seasoning or aging to the paper machines. These measures have taken many different forms from the precipitation of small globules of pitch on the fibers by the use of alum in the grinder showers in the case of the production of mechanical pulp to the use of polyphosphates and other chelating compounds to sequester multivalent ions believed to contribute to pitch precipitation and agglomeration into particles of a troublesome size as well as passivate the solid surfaces in the pulp and paper machine by phosphate treatment so that the adherence of pitch to such surfaces is reduced. Surfactants and dispersing agents of various types also have been used as well as emulsifiers, protective colloids and adsorbents, such as very finely divided talc and china clay. However, it is well recognized that there have been no general treatments or theories which consistently provide a solution to the pitch problems of the pulp and paper industry.

It is a principal object of the present invention to provide an improved process for the control of pitch.

It is another object of our invention to provide a composition that will, when it is added in small amounts to the aqueous fluids of pulp and papermaking systems containing pitch, materially reduce the troubles caused by the pitch.

Other objects and advantages of the invention will become apparent as the description proceeds.

To the accomplishment of the foregoing and related ends, this invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.

Broadly stated, troubles caused by the presence of pitch are inhibited by adding to the aqueous fluids of the pulp and papermaking systems a composition comprising N,N- di-methylamides of straight-chain unsaturated carboxylic acids.

Before proceeding with specific examples illustrating our invention, it may be well to indicate in general the nature of the materials required in the process.

Suitable N,N-dirnethylamides of straight-chain carboxylic acids are those prepared from carboxylic acids containing 18 carbon atoms. The acids are further characterized by having at least one carbon to carbon double bond. Specific acids classified within this category inul ude: oleic, linoleic, linolenic, ricinoleic, and mixtures thereof. Also suitable are the mixed acids found in tall, castor, corn, cottonseed, linseed, olive, peanut, rapeseed, safflower, sesame, and soybean oils. A mixture of carboxylic acids particularly suitable for use in our invention is that available commercially as tall oil fatty acids under the trademark Unitol ACD. A typical analysis of this product is as follows:

TABLE 1 Specification Typical range analysis Fatty acids, pct 98 8-99. 7 98. 9 Rosin acids, pet l 0. 2-0. 6 0. 5 Unsaponifiables, pct 0. 1-0. 6 0.6 Linoleie acid, pct z i 45 Oleic acid, pet z 51 Saturated acid, pet 2. 0-2. 8 2. 4 Acid number 198-201 199 Saponification numbv 198-202 200 Color, Gardner. 34 3+ Viscosity:

SSU, 100 F Gardner, seconds 0.9 Specific gravity, 60 F./60 F. 0. 905 Titre, c 0. 0 Flash point, F, 375 Fire point, F... 435

The amount of the pitch control composition of our invention to be added to the pulp and paper systems is dependent upon the amount of pitch present in the pulp or paper furnish flowing through the systems, to some extent where the inhibitor is added to the system and the amount of white water containing inhibitor that is lost between the point of addition and the end of the system throughout which pitch control is desired. In general, it has been found adequate to maintain a concentration of the pitch control composition of about 0.2 to 20 parts of the inhibitor per million parts of pulp and water or paper furnish and water based on the point of maximum dilution in the system with the preferred range of use from 0.5 to parts per million of the composition. It is understood, of course, that larger quantities of the composition may be used, but such is not generally desirable because costs may be increased thereby without commensurate additional beneficial results.

While we do not wish to be bound by any theory as to how our results are produced, we believe the primary action of the N,N-dimethylamides of the straight-chain unsaturated carboxylic acids is one of coating the small pitch globules or particles with a very thin film which markedly reduces the tendency of the particles to aggregate into ones of troublesome size or to adhere to various solid surfaces of metal and other materials throughout the pulp and paper systems. In addition, evidence has been obtained that, at least under some conditions, already aggregated pitch particles of readily observable size are dispersed by the action of the pitch control composition. Whatever the exact nature of the action of the composition, the pitch particles are maintained in a dispersed state and do not grow in size or adhere to the surfaces of equipment in such a way and to such an extent as to cause the problems encountered when the composition is not added to the pulp or paper systems.

In order to disclose the nature of the invention still more clearly, the following illustrative examples will be given. It is understood, however, that the invention is not to be liimted to the specific conditions or details set forth in these examples, except insofar as such limitations are specified in the appended claims.

Example 1 In a paper machine system making 27.5 pound glassine from bleached semichemical, bleached kraft and unbleached sulfite pulps and repulped broke, in which the pH of the aqueous fluids ranged from about 4.3 to 6.2 and the temperature from 77 to 124 F., considerable pitch trouble was encountered after a short period of operation with no pitch control composition in the system. This was evidenced particularly by sticking on the second press. Mixed N,N-dimethylamides of tall oil fatty acids then were added to the system at the suction side of the fan pump delivering paper furnish to the headbox of the paper machine at the rate of 0.43 pound of the pitch control composition per ton of paper produced, which was equivalent to a concentration of about 1.1 parts of the composition per million parts of the furnish at the wire of the paper machine. This quantity of the mixed amide was not only effective in preventing further deposition of pitch but the pitch which had been deposited on the second press in the absence of the pitch inhibitor disappeared.

Example 2 In a paper machine system making 20.0 pound soap wrap from bleached semichemical and bleached kraft pulps, in which the pH of the aqueous fluids ranged from 4.6 to 6.5 and the temperature from 77 to 142 B, there was no evidence of characteristic pitch problems during the entire run while the N,N-dimethylamides of tall oil fatty acids were added to the paper machine system at the suction side of the fan pump at a rate of 0.63 pound per ton of paper produced. This rate is equivalent to a concentration of about 1.5 parts of the pitch control composition per million parts of the furnish at the wire of the paper machine.

Example 3 In the production of 35.0 pound greaseproof from bleached sulfite and bleached kraft pulps in a paper machine system in which the pH of the aqueous fluids ranged from 3.8 to 5.2 and the temperature from 60 to 138 F., a large amount of pitch deposited upon the wire of the paper machine within a period of several hours when no pitch control composition was added to the systern. The amount of pitch on the wire required stopping the machine to clean the wire with steam. When operation was resumed, the N,N-dimethylamides of tall oil fatty acids were added to the system at the suction side of the fan pump delivering paper furnish to the headbox of the paper machine at a rate varying from 0.47 to 0.51 pound per ton of paper produced, which was equivalent to a concentration of about 1.2 parts of the pitch control composition per million parts of the furnish at the wire of the paper machine. No pitch troubles were encountered during the second run while the pitch inhibitor was being added even after 24 hours of operation.

Example 4 In a paper machine system making diflFerent grades of unbleached kraft board, in which the pH of the aqueous fluids ranged from 4.5 to 6.0 with an average temperature of about F., deposits accumulated in the secondary headbox and these seemed to act as binder for fiber. The total accumulation on the slice of the headbox then would break loose periodically and cause the sheet to break. This had been so severe that the machine had been stopped and the secondary headbox washed as often as once per day in addition to the lost time from breaks. Analysis of the deposit showed that it contained pitch. The subsequent addition of about 1.0 part of N,N-dimethylamides of tall oil fatty acids per million parts of the furnish to the suction side of the fan pump serving the secondary headbox was sufficient to overcome the problem.

Similar results are obtained by the use of the dimethylamides of the fatty acids listed in the foregoing.

The invention having thus been described, what is claimed and desired to be secured by Letters Patent is:

1. A pitch control process which comprises adding to the aqueous fluids of a pulp or papermaking system a composition consisting essentially of an N,N-dimethylamide of a straight'chain carboxylic acid, characterized in that said acid contains 18 carbon atoms and at least one carbon to carbon double bond, at a rate which provides a concentration of said amide of at least 0.2 ppm. in said aqueous fluids.

2. The process of claim 1 wherein the straight-chain carboxylic acid is a mixture of straight-chain carboxylic acids containing 18 carbon atoms and at least one carbon to carbon double bond.

3. The process of claim 1 wherein the straight-chain calrboxylic acid is a mixture of acids derived from tall or 4. The process of claim 1 wherein the straight chain carboxylic acid is a mixture of acids derived from linseed oil.

5. The process of claim 1 wherein the straight-chain carboxylic acid is a mixture of acids derived from soybean oil.

6. The process of claim 1 wherein the straight-chain carboxylic acid is a mixture of acids derived from cottonseed oil.

7. The process of claim 1 wherein the straight-chain carboxylic acid is a mixture of acids derived from corn oil.

8. The process of claim 1 wherein the straight-chain carboxylic acid is a mixture of acids derived from peanut oil.

N,N-dimethyl- N,N-dirnethyl- N,N-dimethylamide is N,N-dimethylricinoleamicle.

6 References Cited by the Examiner UNITED STATES PATENTS 8/1965 Buckman et a1 162199 X 9/1965 Koebner et al. 252-357X DONALL H. SYLVESTER, Primary Examiner. HOWARD R. CAINE, Examiner. 

1. A PITCH CONTROL PROCESS WHICH COMPRISES ADDING TO THE AQUEOUS FLUIDS OF A PULP OR PAPERMAKING SYSTEM A COMPOSITION CONSISTING ESSENTIALLY OF AN N,N-DIMETHYLAMIDE OF A STRAIGHT-CHAIN CARBOXYLIC ACID, CHARACTERIZED IN THAT SAID ACID CONTAINS 18 CARBON ATOMS AND AT LEAST ONE CARBON TO CARBON DOUBLE BOND, AT A RATE WHICH PROVIDES A CONCENTRATION OF SAID AMIDE OF AT LEAST 0.2 P.P.M. IN SAID AQUEOUS FLUIDS. 